See also Response 200

The instrument is a modern processor controlled, combined push button telephone, single tape answering and recording machines with remote interrogation. The instrument may stand on a flat surface or desk top provided by the customer, or be wall mounted if required. To wall mount, the bracket on the base is turned around so that the key hole slots face towards the top of the instrument. Two fixing screws must be provided which will locate in the key hole slots.

A unique feature of the BT Response 400 at present, is that the outgoing announcement is digitally recorded giving consistently high quality recording and fast reset at the end of a call. A single tape is used for incoming messages, and the outgoing announcement is also recorded on tape to act as a back up should the power supply fail. The recorded outgoing announcement is then automatically transferred to the voice IC of the machine once the power is restored for normal operation.

The facilities of the instrument are as follows:-

- Desk or Wall mounted. Lug on case provides off hook position for handset when wall mounted.

- Loop or MF4 Signalling. Switchable by the customer.

- Mixed signalling. If set for LD signalling, pressing * (star/tone button) will change signalling to MF4 until call is cleared.

- Recall. Earth Loop / 10OmS timed Break. Switchable by customer.

- Last number Redial. Up to 32 digits. A pause, * (star) or recall signal counts as a digit.

- Transfer Redial memory to permanent memory.

- Latching Secrecy Button with LED indication.

- Dial Pause, 4 seconds. (Pause button is under tape compartment cover)

- Memory Stores. 20 one touch. Up to 16 digits inclusive of any signalling change, pause and TBR recall instruction. Note:- Memory stores and LCD display are powered by a single 9 volt battery.

- Call Timer capability.

- Message Tape. Standard MC-60 Microcassette. Up to 30 minutes recording time.

- Normal Outgoing Announcement (Answer & Record) - Digitally recorded. Up to 16 seconds of high quality recording, or 32 seconds of lower quality.

- Answer Only Announcement - Up to 30 seconds.

- Outgoing Announcement Check - normal or private playback and record through handset.

- Automatic soft switch to Answer Only when the message tape is full. An Answer Only Announcement must be recorded to use this facility, otherwise the machine will not answer, making remote interrogation impossible.

- Memo. Up to 30 seconds with separate LED indication, replay and pause facility.

- Built in microphone - Used for announcement and Memo recording. May record privately using the handset)

- Play messages - Press Play, to Pause press Play again. To play all messages to end of tape, press Play twice more when tape has stopped.

-Incoming Message up to 3 minutes.

- Skip Announcement - Frequent callers can key '*' from an MF4 telephone or remote interrogator and leave a message without having to listen to the outgoing announcement.

- Two digit LED display - Indicates messages, 0 to 99 and machine status.

- Volume Control - From minimum to maximum volume.

- Call Screening (Monitoring) - Listen to incoming callers leaving message. The volume control must be turned up to listen.

- Two way recording. A security tone is given every 15 seconds.

- Automatic Message Save when interrogated remotely.

- Fast Message tape Forward, Rewind and Erase.

- Cleared Detect. Line break stop. Clear Detect switch ON or OFF.

- VOX - (Voice Operated Switch) release from line. Low or High sensitivity switchable by customer. Sensitivity switch LO or HI.

- Ring Adjuster - 2, 6 or TS (Time Saver). TS = Answers after 2 rings if messages have been left, or 6 rings if no messages. This facility aids remote interrogation. i.e. When interrogating remotely, if the call is not answered after 2 rings, the caller can clear down knowing there are no messages and save the cost of a call.

- Remote set to Answer - Call machine and let it ring 20 times.

- Branchphone reset - Will release machine from the line should a parallel telephone handset be lifted. Inhibited for a short period (3 seconds) before and after answering.

- Paytone Detection - Up to 15 seconds delay of announcement if paytone is present.

- Remote Interrogation with a customer programmable 2 digit security code 00 to 99.

- Remote Interrogation Inhibit - Set Remote Interrogation switch to OFF.

- The customer may keep a library of tapes that have been pre recorded with different announcements. The tape must be changed with the machine POWERED UP for correct operation.

The handset and keypad are line powered. The Loudspeaking facility and answering/recording features of are mains powered from the 9.5 volt dc plug top transformer.

In the event of a mains failure all mains dependent facilities cease to function. Restoration of the mains supply will automatically reset the machines to answer whether or not they were set to "answer" before the supply failed.

This is a system default condition and cannot be overridden. Messages received before the power failure are not lost and can be played back remotely or by using the play button on the machine.

Made by Inventa Electronics

Distributed by BT Districts. Supply on both Rental and Sale terms. Sold machines can be offered a BT maintenance agreement. BT UK Trade Sales, sale only.

Approval Number S/2981/3/L/502 011

Approved DEL, PBX CAT 1, 3, 5 & 7.

Approved as supplied for connection to Public Switched Telephone Networks (PSTN) and 2-wire PBX extensions.

User Guide TPU 1403
Quick Reference Guide TPU 1404
Remote Interrogator User Guide TPU 1405
Product Manual PDM/TPM/A010

A Phone Socket and a 240 volts, 13 amp, 50 Hertz mains supply socket are required within easy reach of the instrument. Transformer lead and Line Cord both measure 300Omm.

Suitable for use on Phone Socket installations on DELs and most types of 2- wire PBX extensions.

Ringer Equivalence Number (REN) is 1. See, CFN 007 Telephones for further REN details.

The instrument does not contain any on-site serviceable parts. Therefore maintenance is limited to functional testing, checking the facility switches are set to provide optimum performance of the instrument to match the line to which it is connected, the condition of the tape and that the tape head is clean.

If the machine fails completely, the output voltage of the Transformer should be checked. The Transformer output is marked 9.5 volts dc, but will measure about 13 volts when tested with the output open circuit.

The User Guides recommend that the customer should perform the following routines:-

Every three months, turn the tape over and re-record the outgoing announcement.

Every six months, clean the tape head using a cotton bud moistened with a proprietary tape head cleaning fluid and replace the tape.

Any high quality "normal bias" MC-60 size Microcassette is suitable. Although available, longer and shorter tapes must not be used as they will prevent the instrument from operating correctly.

The duration between the above routines should be reduced if the machine is heavily used.

The user should replace the PP3 battery at yearly intervals, or when the Batt Low symbol is displayed on the LCD.

New units carry a 21 months warranty from the date of manufacture as shown on the year and week marking on the base of the instrument. These markings form the first 4 digits of the serial number.

British Telecom guarantee sold machines (excluding cassette tape and battery) for 12 months from the date of purchase irrespective of the date of manufacture.

Decryption                                 		BT Item Code
Response 400 Combined LST / Ans & Rec Machine         	870470
(Complete with transformer, tape and PP3 battery)
BT Remote Controller No 2 (MF4) 			870427
Transformer 9.5 volts dc                                870471
Message Tape MC-60 Microcassette.                       870435
Or any high quality, normal bias MC-60 tape.
9v volt Alkaline PP3 size battery. 			171419

Normal test conditions when waiting to answer. After answering the telephone and answering machine presents a loop resistance to line of approximately 3280 ohm measured at 28mA. Additionally, the instruments will draw about 25ma on hook. This may appear to give apparent Low Loop line test conditions. With the handset off hook, like many modern telephones, they may give high resistance telephone loop test conditions.

Instant reset once machine has released from the line. The only delay in answering a following call is the number of ring cadences set on the ring set switch i.e. 2, 6 or TS. TS = 2 after message received, or 6 with no messages.

The ringing circuit has been designed to recognise both PSTN and all internal ringing cadences generated by BT PABX's. There is no manual ring facility.

3. VOICE / TONE DETECTION (Voice Operated Switch - VOX)
The VOX will release the machine from the line after approximately 7 seconds of quiet, constant or cadence Network tone (i.e. dial tone, NU etc). The VOX sensitivity has a High and Low Sensitivity switch provided. The normal switch position is High. In this position it is possible that line noise may be detected as speech. If this happens the machine will record line noise up to its maximum message length. A Low setting is therefore provided for use in cases where line noise causes persistent problems.

4. CLEAR DETECT Line Break Clear/Release from line
Modern exchanges generate a 100 ms line break on the called parties line when the calling party clears down, this is a called a disconnect clear signal. Both machines will detect this signal and immediately release from the line without the need to wait for network tones.

When the machine answers the line, it checks whether paytone is present. If paytone is detected, the announcement is delayed for up to 15 seconds.

This facility causes the machine to release the line when a telephone connected to the same line is taken off hook. For about 3 seconds before and after answering this facility is inhibited. This prevents the false release of the machine from line due to line ringing (current surge to & fro) when answering.

Response 400 provides the facility for remote interrogation using a 2 digit customer programmable security code from 00 to 99. If no code is set the machine will default to 00. To provide total security where the customer does not require or use remote interrogation, the facility can be turned off by setting the Remote Interrogation on/off switch to OFF.

Remote interrogation is achieved by using a BT Remote Interrogator or MF4 telephone to enter the security code any time after the machines have answered, and then further instructions as per the user guide.

On-site maintenance of the Response range is limited as the equipment contains no serviceable parts. Some routine servicing - detailed in the User Guide should be carried out by the customer, but field maintenance is restricted to checking the facility switch settings and testing the power unit output.

Several adapters used with Response instruments are marked with lower outputs than those actually measured. Approximate voltage readings (with the output open circuit) are as follows:-
Transformer 19B (marked 13.5V DC) measures 19 - 20v.
Transformer 752 (marked 9V AC) measures 11 - 12v.
Transformer 753 (marked 9.5V DC) measures 13 - 14v.


It has been reported that a large quantity of the Response range of TARMs have been returned as faulty without being fully reset and retried. Some faults are caused by quick line disconnects and Radio Frequency Interference and may be cleared by a reset.

Models such as the Response 200, 300, 400, 500 & 1000 have all got a reset button on the underside of the unit. Depressing this button momentarily, using a small probe, will perform a slightly different reset to that performed when the mains is turned off/on. It is suggested that this is performed first, then retry all facilities, before changing out the unit.

However, if after changing the unit the same fault recurs on the new unit, the problem may be site specific and changing the unit again will be of no advantage. If this is the case, please contact the Technical Helpdesk for further advise.

A major problem with Response TARMs recording after a message has been left has been caused by the exchange equipment presenting ‘clicks’ on the line when it is idle. This is due to a modified line card on System X exchanges. BT Labs are aware of the problem and are investigating a cure. Changing the unit will not clear this problem. 

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Last revised: December 19, 2010